1. Field of the Invention
The present invention relates to a substrate and semiconductor light emitting device. More specifically, the present invention relates to a non-polar hetero substrate, a method for manufacturing the same, and a nitride-based light emitting device using the same.
2. Discussion of the Related Art
Gallium nitride used as a material for semiconductor devices such as blue light emitting diodes has a Wurzite crystal structure, which is mostly grown into a thin film in a c-surface crystal direction. The reason is that crystal growth in the c-surface crystal direction facilitates horizontal growth and high-quality thin films with little defects (such as dislocation) can be obtained.
At this time, a crystal structure in which nitrogen layers and gallium layers repeatedly cross each other based on growth direction is present. Accordingly, strong internal field is present between nitrogen and gallium, thus causing a polarization phenomenon.
The formed internal field is divided into two components, spontaneous polarization and piezo-electric field. When layers having different lattice constants such as InAlGaN are inserted, polarization effects increase and quantum confined stark effects may occur.
For example, in a structure in which an InAlGaN active layer is inserted between p- and n-type GaN layers, such as blue light emitting diode, deformation between layers is caused by the difference in lattice constant. This causes generation of internal field and bending of an energy bend structure of the active layer.
As a result, wave functions of electrons and holes in the active layer are sparially separated and the size of energy gap decreases, which may be main factors of deterioration in recombination efficiency.